An investigation's been launched into a dramatic armed robbery in Dublin.

At about 7:45pm yesterday a man armed with a knife entered a newsagent's in Crumlin on the Long Mile road and demanded cash.

The man is understood to have fled the scene after threatening staff and got onto a Dublin Bus which was going into Dublin City.

A witness alerted Gardaí and a number of units responded and the bus was stopped at James street and a man arrested a short time later.

A knife has been recovered and a man is being detained at Crumlin Garda Station.